1. Field of Invention
This invention relates to fluorinated .alpha.-carboxylic-.omega.-carbonyl fluorides and the preparation of fluorinated vinyl ether monomers therefrom.
2. Prior Art
Fluoromonomers having the general structure ##STR3## wherein Y is --C.sub.n F.sub.m H.sub.1, where n, m, 1 are zero or positive numbers which satisfy the requirements of a difunctional fluorinated hydrocarbon residue, and A is a functional group including --COOR, --SO.sub.2 F and --COF, are disclosed in German application No. 2,504,622, issued Aug. 7, 1975.
Fluoromonomers of the above general structure in which A also includes --CN are disclosed in Ger. Application No. 2,659,581, issued July 13, 1977.
No method of preparing the above monomers is provided in either of the above applications. The first disclosures of a preparative method of which we are aware are contained in Ger. Application No. 2,635,312, issued Feb. 17, 1977, Japanese Application No. J5-2,003,017, Serial No. JA 079326, issued Jan. 11, 1977, and Japanese Application No. J5 2,105,118, Serial No. JA 020144, issued Sept. 3, 1977. Taken together, these applications describe the reaction of perfluoroalkyl diiodides I(CF.sub.2).sub.n I, where n = 3-5 , with fuming sulfuric acid to form a lactone; reaction of said lactone with HFPO to form a .alpha.-.omega. diacylfluoride; and conversion of the diacylfluoride to esters of the formula ##STR4## wherein R.sub.F is perfluorinated alkyl of 1-10 carbon atoms and n = 1-5, preferably 1-2.
Fluoromonomers having the general structure CF.sub.2 =CFO(CF.sub.2).sub.n --X, where X includes --CO.sub.2 R and --CN, R = H or alkyl of 1-10 carbon atoms, and n = 2-12, preferably 2-4, are disclosed in U.S. Pat. No. 3,546,186 issued Dec. 8, 1970. Such monomers are useful in preparing fluorohomopolymers or copolymers with tetrafluoroethylene, but have been difficult to make from symmetrical compounds such as FOC--(CF.sub.2).sub.n --COF.
Symmetrical difluoromalonic compounds of the formula CF.sub.2 Q.sub.2 where Q may be COOH, COOalkyl or COF are known (E. J. P. Fear et al., J. Appl. Chem., 5, 589-594 (1955); and J. Heicklen, J Phys. Chem., 70, 618-627 (1966)). Ryazanova et al., Zh, Vses. Khim. Obschchest, 1972, 17, No. 3, 347-8, describe compounds of the formula ROOC(CF.sub.2).sub.n COF where n is 3, 4 or 6.
Fluoromonomers having the formula ##STR5## are disclosed in U.S. Pat. No. 3,282,875, issued Nov. 1, 1966. Preparation of these monomers by reaction of FSO.sub.2 --CF.sub.2 --COF with hexafluoropropylene oxide (HFPO) is disclosed in U.S. Pat. No. 3,301,893, issued Jan. 31, 1967.
Fluoromonomers of the formula ##STR6## containing secondary --CN groups are disclosed in U.S. Pat. No. 3,852,326, issued Dec. 3, 1974. Such monomers are prepared by reacting ##STR7## with HFPO.
Conversion of fluoromonomers of formula ##STR8## to carboxylated monomers of formula ##STR9## is disclosed in Japanese Application J5 2053-814, Serial No. JA 129691, issued Apr. 30, 1977.
Fluoropolymers having the formula ##STR10## where A is an acid group which includes --COOH and --SO.sub.3 H, are disclosed in U.S. Pat. Nos. 3,853,720 and 3,853,721, issued Dec. 10, 1974. These patents do not disclose a method of preparing the fluorinated vinyl ether monomers.